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wire size for conduit run

11K views 25 replies 4 participants last post by  WDR 
#1 · (Edited)
Hi evereryone, I am planing on running aproximatly 50 feet of wire in conduit to power two 240 volt pumps, according to the labels on the motors one draws 21 amps and one 26 for a total of 47 amps. I plan on using 4 wires as some of the controls are 120 volt. I plan on using thhn wire runing of a 60 amp double pole fuse approximatley 25 feet thru a basement in liquid tite flexible metalic conduit and then continuing outside underground in conduit for approximatley 25 feet. Dose this all sound good? Now for the questions
-What size wire should be used?(the ambiant temperature gets up to about 100 degrees fahrinheit)
-Can I use the liquid tite flexible metalic conduit for the under ground run?( part of it will be above ground and exposed to sunlight)
-And what size conduit would I need ? Thanks for your help.
 
#2 ·
Unless someone on here has all the charts for the calculations involved you should probably have an electrical contractor do the installation. You need the starting amps for each motor and then need to do a voltage drop calculation for the distance involved just to size the wiring. Each of those motors should be on separate breakers or fuses sized for that motor. I did these calculations 35 years ago but would never try to do so today.
 
#4 ·
conduit

I will have each of the motors on a seprate breaker on the end of the run the pumps ar for irrigation and the run may actually be less than 50 feet probobly more like 40. I asked about this because I do not have the charts but I am aware of voltage drop and other similer factors.The only amp ratings I have are the tags on the pumps. I am located in murphysboro, IL. thanks again!
 
#5 ·
My pool pump has a MAX rating of 18.6a @ 120v, 9.3A @ 240v

If that is the Max amp rating on the pumps then you need #10 wire & a 30a breaker for each

You need THWN for wire for outside
50' is not a problem for voltage drop

Does the pump have a place for 4 wires ?
Or are you going to run a sub-panel & put breakers in to power pumps & other 120v loads ?
 
#7 · (Edited)
pumps

I plan on installing 4 wires running to the pumps with a control panel the only load on this panel would be the pumps and some 110 controlls I can run either of the pumps of of a set of 30 amp fuses with no problems but I have to run one 60 amp to the controll panel because the only oponing in the 200 amp main fuse panel is for 2 60 amp fuses. one of my concerns was that I do not know the temp rating of the fuse box and would have to derate the thhn and use thicker wire.each pump would have its own protection at the control panel
 
#8 · (Edited)
pumps

My questions where
-what size thhn hots, neutral, and ground do I need taking into account the old fuse box, the conduit, and that it gets up around 100 degrees fahrenheit outside in the sun
- can I use the metalic water tite flex under ground and what size do I need.
 
#9 ·
Ok I think I understand what your doing now. To get this right there are a few calculations that may take me some time maybe 30 minutes or so.

Do you know the horsepower of each motor?
 
#10 ·
motors

Ok I will go over the whole thing again starting at a 200 amp fuse panel with a double 60 amp fuse in the basement run 25 feet thru flexible liquid tite metalic conduit go under ground for about 15 feet then to the controll panel with 2 30 amp fuses for each pump.some other details below
-the pumps are each 5 horse power and either one runs with no problems on a 30 amp circuit.
- 220 with 4 wires as some of the controlls use 110
-the wire will be type thhn(this wire is also rated as thwn and mtw)
now the questions again.
- what size hot neutral and ground wires are needid taking into acount the fuse box with a unknown temp rating, the conduit, and that the ambiant temputure exceeds 30 degrees Celcius( it gets to about 100 degrees F in the summer)
- can the flex conduit go under ground and what size do I need. thanks for everyones help!
 
#11 ·
Conductor size and feeder protection are taken from tables that show an flc for a specific horsepower not what is on the motor nameplate. Which is why I asked for the horsepower of the motors.

We can use the motor nameplate fla and get pretty close and I am assuming your motors have overload protection located internal to the motor and the 30 amp fuses (not circuit breakers) are for overcurrent and ground fault protection.

If you have the horsepower of the motors it would be a better calculation.

Back after lunch .. post the hp if possible
 
#13 · (Edited)
Not a problem. If we use the motor tables for 5 hp your flc (full load current) is 28 amps for both motors.

Lets do the branch circuit circuit conductors from the controller and the fuse blocks first.

For branch circuit conductor size the calculation is ... 1.25 x 28 = 35 amps minimum this would be a #10 thwn at 75C or a #8 thwn at 60C terminations installed in conduit. You must assume 60C if that is unknown.

The fuses in the controller fuse blocks would be 1.75 x 28 = 49 amps so maximum is 50 amp time delay fuses for 5 hp motor. You can go with less if you want as long as they do not blow when the motor starts.

For the feeder

The feeder conductor size is (28 x 1.25) + 28 = 63 amps this would be a #6 awg thwn if 75C terminations or #4 awg if 60C terminations.


Feeder over current protection would be 50A + 28 A = 78 amps ..must chose the next size down for a feeder so a 70 amp fuse maximum for feeder protection. You can use a 60 amp since that is your largest you say you can install.

Ground wire for the feeder can be # 10 copper

Conduit size feeder

3 #6 awg with a #10 ground in liquid tite = trade size 3/4" minimum suggest increase one trade size

Same for sch.40 pvc

For any areas above ground exposed to physical damage you need sch. 80 pvc this will require 1" sch.80

I wouldn't use the lfnc to go underground but it can be listed for that. It would be better to use sch. 40 pvc for that portion of the run.

For 3 #4awg thwn + #10 ground use minimum 1 " for all raceways
 
#16 · (Edited)
wire

I have some #10 type tw wire. Could I run 5 of these thru conduit from the control pannel about 6 feet to the pumps, 2 hots for each pump and one ground for both.Part of the conduit will be shared by both pumps. What size conduit? also what size and type of copper or aluminium cable could be used in place of the conduit and thwn in the basement and or underground ? In the basement it would be on the ceiling so I would not consider it subject to physical damage. and lastly what is the proper way to terminate the aluminium cable. thanks again!
 
#17 · (Edited)
I have some #10 type tw wire. Could I run 5 of these thru conduit from the control pannel about 6 feet to the pumps, 2 hots for each pump and one ground for both.Part of the conduit will be shared by both pumps. What size conduit? also what size and type of copper or aluminium cable could be used in place of the conduit and thwn in the basement and or underground ? In the basement it would be on the ceiling so I would not consider it subject to physical damage. and lastly what is the proper way to terminate the aluminium cable. thanks again!
#10 copper most likely would be fine ... tw however is a 60C wire insulation so the fuse blocks need to be rated for 60C or 60C/75C. In other words if the fuse blocks are rated 75C only you cannot terminate a 60C insulated wire to those fuse blocks.

Minimum conduit size for 5 tw #10's is 3/4" for all raceways.

I not familiar with any aluminum multiwire cable with outer sheath that would be applicable for direct burial.

You can use copper uf-b cable or copper power cable type TC or MC cable . I prefer type TC power cable.
 
#19 ·
You would need #4 aluminum in conduit to meet the ampacity requirements of the feeder. USE-2 al can be direct buried but would need to be in conduit above grade and the run to the panels.

I always recommend a conduit installation with individual copper conductors if length is not to excessive.

My second choice would be USE-2 using conduit above grade. Be sure your fuse block will accept the bigger wire.

My third choice would be power type TC copper cable 3 conductor with ground this will avoid any splicing in J boxes since it is direct bury rated..
 
#20 ·
cable

I thing I will go with copper in a conduit as the run is fairly short. If I was to go with a nother method what would be the most affordable that you would recommend? and thank you very much for all of your help with this project.
 
#21 · (Edited)
#23 ·
If I used tc cable would it need conduit? and what gauge would I need also do you know anywhere to get it near murphysboro, IL
Nope no conduit required, treat it just like uf-b ... burial depth should be 24".

Any electrical supply has it or can order it in.

To comply with code and proper design and unknown terminal temperature ratings at the fuse box you will need #4 . However you say you can only install a max 60 amp fuse so if that doesn't change IMO you can use #6 at 55 amps 60C terminations. TC power cable is rated 90C but generally we use the 60C ratings for ampacity . Some will argue that TC can use 75C and 6 awg would then let you use 65 amps. Anyway IMO you will be fine with #6.
 
#24 ·
fuse

#4 would be fine because the fuse terminals are rated up to #2 aluminum and #4 copper however one cable company I found online only has it up to #10 also if I was able to change the run and remove the underground pard could I use 2-2-2-4 type SER aluminum cable?
 
#25 ·
#4 would be fine because the fuse terminals are rated up to #2 aluminum and #4 copper however one cable company I found online only has it up to #10 also if I was able to change the run and remove the underground pard could I use 2-2-2-4 type SER aluminum cable?
Yes that would be fine if you do not bury it and do an overhead feeder to the pump house. IMO you want to use a wiring method that is continuous without splice from the basement fuse panel to the pump controller. It wouldn't hurt to have that feeder terminate in a disconnect at the pump house then to the controller ..in fact it is likely required. As is a grounding electrode.
 
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